Circuits for boosting DC voltage using a RF input signal are known. In some of these circuits, a rectifier technique is used to generate the boost voltage using the RF input signal. For example, see “A High-Power Handling GSM Switch IC With New Adaptive-Control-Voltage-Generator Circuit Scheme” by Keiichi Numata et. Al., 2003 IEEE Radio Frequency Integrated Circuits (RFIC) Symposium, Philadelphia, Pa., Jun. 8, 2003. In addition, U.S. Pat. No. 7,263,337 discloses a RF switch that is allegedly capable of operating in a highly linear manner in response to a low control voltage. U.S. Pat. No. 7,263,337 discloses a bias circuit that includes a rectifier having an input, an output and a DC control voltage input, wherein the rectifier is configured to produce the rectifier output, while providing a substantially high input impedance at the rectifier input, a rectified voltage from an alternating input signal applied at the rectifier input; and a bias extractor having an extractor input, a control voltage input and an extractor output, coupled to the rectifier output, and being configured to produce at the extractor output a DC voltage that is greater in magnitude than the DC control voltage input. Thus, in this patent, the RF energy is rectified by a diode and added to a control signal to the switch. These known methods are useful for a limited range of module conditions, but have some issues when considering a broader range of operating conditions.
The most notable issue with U.S. Pat. No. 7,263,337 is that there is no immunity to the switch control voltage that is generated if a Voltage Standing Wave Ratio (VSWR) mismatch is applied to the module. The amount of variation in the switch control voltage will be dependent on the location of the rectification circuit and could potentially diminish its effectiveness if the switch control voltage drops below a voltage supplied by a battery (VBAT). Another issue with the implementation in U.S. Pat. No. 7,263,337 is that the rectified voltage is “hardwired” to the switch control voltage.
Thus, it would be beneficial to have a transmit module that has improved system level harmonic performance under mismatch load conditions at switch antenna ports.